Petrogenesis and redox state of late Mesozoic granites in the Pingmiao deposit: Implications for the W–Cu–Mo mineralization in the Dahutang district
Petrogenesis and redox state of late Mesozoic granites in the Pingmiao deposit: Implications for the W–Cu–Mo mineralization in the Dahutang district
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平庙矿床晚中生代花岗岩岩石成因及氧化还原状态：对大湖塘地区W-Cu-Mo矿化的启示
DOI：
10.1016/j.oregeorev.2022.104898
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发表时间：
2022-04
影响因子：
3.3
通讯作者：
Dewei Liu
中科院分区：
文献类型：
--
作者：
Yanshen Yang;Xiaofei Pan;Zengqian Hou;Yang Deng;Zhiyu Zhang;Xianke Fan;Xin Li;Dewei Liu
平庙钨（铜）存款矿床位于华南新发现的大湖塘大型矿集区中部。野外对比和矿物组合证实，坪庙存款钨（铜）矿化与晚中生代多期花岗岩（含斑状二云母花岗岩、黑云母花岗斑岩、细粒白云母花岗岩和锂云母钠长花岗岩）有成因联系。锆石U-Pb定年结果表明，这些花岗岩侵位于约1000年。146-143 Ma，与大湖塘地区其他矿床的含钨铜钼花岗岩类同时代。强过铝质（A/CNK > 1.1）、Rb与Th、Rb与P2 O 5的负相关性、低Zr + Nb + Ce + Y值（大部分低于200）和较低的Zr饱和温度（低于800 °C）表明这些花岗岩为典型的S型花岗岩。这些花岗岩显示出相似的Nd同位素（−8.91至−4.61），CaO/Na 2 O（0.2-0.57）和Al 2 O3/TiO 2与大湖塘地区其他矿床的含钨、铜、钼花岗岩类相比，表明它们是双桥山群变岩部分熔融的产物（或与双桥山群地球化学性质相似的元古宙变质基底），并有少量镁铁质-超镁铁质火山岩的侵入。全岩和云母记录的地球化学分馏趋势可以区分从斑状二云母花岗岩和黑云母花岗斑岩到细粒白云母花岗岩和锂云母钠长石花岗岩的演化趋势。明显的稀土元素四分体效应、高Li和F含量、低K/Rb、Zr/Hf和Nb/Ta比值以及云母的环带特征，表明锂云母钠长石花岗岩形成过程中存在熔体-流体相互作用。平庙花岗岩具有还原氧化还原状态，表现为全岩Fe_2 O_3/FeO比值低（大部分<0.5），黑云母Fe_3 +/Fe_2+比值低（0.02-0.07），锆石Ce_4 +/Ce_3+比值低（中值18.70），氧逸度低（接近或低于FMQ缓冲区）。大湖塘地区晚中生代花岗岩类是钨、铜（<1 Mt）、钼（<0.3Mt）成矿的有利场所。值得注意的是，更进化的锂云母钠长石花岗岩具有W，Sn，Nb和Ta矿化的潜力。
The Pingmiao W (Cu) deposit is located in the central part of the newly-discovered giant Dahutang ore-concentrated district, South China. Field relationships and mineral assemblages confirm that the W (Cu) mineralization in the Pingmiao deposit is genetically related to multiphase late Mesozoic granites, which include the porphyritic two-mica granite, biotite granite porphyry, fine-grained muscovite granite, and Li-mica albite granite. Zircon U–Pb dating shows that these granites emplaced at ca. 146–143 Ma, which are coeval with the W–Cu–Mo-bearing granitoids from other ore deposits in the Dahutang district. The strongly peraluminous (A/CNK > 1.1) feature, negative correlations between Rb and Th and between Rb and P2O5, low Zr + Nb + Ce + Y values (mostly lower than 200), and relatively low Zr saturation temperatures (lower than 800 °C) suggest that these granites are typical S-type granite. These granites show similar Nd isotopes (−8.91 to −4.61), CaO/Na2O (0.2–0.57), and Al2O3/TiO2(mostly ranging of 50–90) ratios with those W–Cu–Mo-bearing granitoids from other ore deposits in the Dahutang district, suggesting that they derived from partial melting of metapelites in the Shuangqiaoshan Group (or the Proterozoic metamorphic basement geochemically similar to the Shuangqiaoshan Group), with involving of minor mafic–ultramafic volcanic rocks. Geochemical fractionation trends recorded by whole-rocks and micas permit to distinguish the evolutionary trend from the porphyritic two-mica granite and biotite granite porphyry to the fine-grained muscovite granite and Li-mica albite granite. The apparent rare earth element tetrad effect, high Li and F contents, low K/Rb, Zr/Hf, and Nb/Ta ratios, as well as the zoned features of micas suggest that the melt–fluid interaction occurring during the formation of Li-mica albite granite. The Pingmiao granites have reduced redox state, revealed by their low whole-rock Fe2O3/FeO ratios (mostly <0.5), biotite Fe3+/Fe2+ratios (ranging of 0.02–0.07), zircon Ce4+/Ce3+ratios (median value of 18.70), and oxygen fugacity (near or below the FMQ buffer). The data in this study indicate that the late Mesozoic granitoids in the Dahutang district are favorable for W, Cu (<1 Mt), and Mo (<0.3 Mt) mineralization. Notably, the more evolved Li-mica albite granite has potential for W, Sn, Nb and Ta mineralization.
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